Proportional-Integral-Derivative:

For processes which could operate within continuous cycling, the associatively inexpensive two position controller is adequate. For processes which cannot tolerate continuous cycling, a proportional controller is frequently employed. For processes which could tolerate neither continuous cycling nor offset error, a proportional plus reset controller could be used. For processes which required improved stability and could tolerate an offset error and a proportional plus rate controller is employed.

Therefore, there are a few processes which cannot tolerate offset error, yet required good stability. The logical solution is to use a control mode which merges the benefits of proportional, reset, and rate action.  This lesson describes the mode identified as proportional plus reset plus rate, generally known PID (Proportional-Integral-Derivative).